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Because learning changes everything.®
Chapter 08
Metabolism
Lecture Outline
HUMAN NUTRITION
Science for Healthy Living Third
Edition
Tammy J. Stephenson, Megan R.
Sanctuary, Caroline W Passerrello
© 2022 McGraw Hill, LLC. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution permitted without the prior written consent of McGraw Hill, LLC.
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8.1 Fueling the Body
Learning Outcomes
1. List at least three forms of energy.
2. Identify the sources of energy for the human body.
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What is Energy? 1
Energy - in living organisms, power derived from sunlight or
food to perform cellular work
• Can neither be created nor destroyed
• Can undergo transformations
• For example, body cells take energy stored in food and convert it
into a usable form of energy
Cellular work - activities in cells requiring energy, such as
building and transporting molecules
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What is Energy? 2
Human cells obtain energy by releasing chemical energy
stored in macronutrients (carbohydrates, lipids, proteins) and
alcohol.
• Energy in food is measured in kilocalories (Calories)
• Cells cannot release energy from vitamins, minerals, or
water
Chemical pathways - specific chemical reactions that occur
in sequences
• Used to access and use energy stored in “biological fuels”
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Assess Your Progress 8.1
1. Identify substances that the human body can use as fuel.
2. Which form of energy is stored in macronutrients?
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8.2 Energy Metabolism
Learning Outcomes
1. Compare and contrast anabolic and catabolic reactions.
2. Identify nutrients that act as coenzymes in energy
metabolism.
3. Discuss ATP, including why it is important and where it is
made.
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Metabolism 1
Energy metabolism is the sum of all the chemical pathways
in the body that break down molecules to release energy and
use energy to build new molecules.
• These chemical pathways enable the human body to
obtain and use energy from macronutrients and alcohol
Metabolic reactions may be catabolic or anabolic.
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Catabolism and Anabolism
Catabolism - metabolic pathways that break down larger
molecules into smaller ones
• Cells transform some of the energy in macronutrients into
usable chemical energy to power chemical reactions.
• The rest is transformed into heat energy
• Cannot be used to perform cellular work, but helps maintain normal
body temperature
Anabolism - metabolic pathways that build larger molecules
from smaller ones
• Requires energy, supplied by catabolic reactions
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Metabolism 2
• Metabolism involves a
continuous transfer of
energy in the body.
• Energy released from
catabolic reactions is
used to fuel anabolic
reactions in cells.
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Roles of Enzymes and Coenzymes
Most chemical reactions that occur in living cells require
specific enzymes that facilitate (catalyze) reactions.
• Enzymes remain unchanged
• Usually require use of coenzyme
Coenzymes - group of organic compounds that assist
enzymes with chemical reactions
• Many B vitamins serve as coenzymes or are components
of coenzymes
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B Vitamins and Their Coenzymes
B Vitamin
Coenzyme
Thiamin
Thiamin pyrophosphate (TPP)
Riboflavin
Flavin adenine dinucleotide (FAD, FADH2)
Flavin mononucleotide (FMN)
Niacin
Nicotinamide adenine dinucleotide (NAD+, NADH,
NADP+)
Nicotinamide adenine dinucleotide phosphate
(NADP+, NADPH)
Pantothenic acid Coenzyme A (CoA)
Vitamin B-6
Pyridoxal phosphate (PLP)
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Energy Shuttles: NAD+ and FAD
Energy in the body is transferred between molecules in the form of
electrons (e–)
Because electrons are negatively charged, they are usually
accompanied by positive hydrogen ions (H+)
Two different coenzymes accept
and transport these ions:
• Nicotinamide adenine dinucleotide
(NAD+) - niacin-containing coenzyme
• Flavin adenine dinucleotide (FAD) –
riboflavin-containing coenzyme
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Adenosine Triphosphate
Adenosine triphosphate (ATP) is a high-energy phosphate
compound that serves as energy “currency” of cells
• Energy released by the break down of macronutrients is
captured in this chemical form
• Comprised of adenosine bound to three (tri-) inorganic
phosphate groups (Pi)
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Adenosine Diphosphate
When an enzyme cleaves the bond between the last two
phosphate groups of ATP:
• Energy is released
• Cells can use energy for anabolic activities
Adenosine diphosphate (ADP) is the molecule that forms
when ATP loses its last phosphate group during ATP
catabolism
• Comprised of adenosine bound to two (di-) inorganic
phosphate groups
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Phosphorylation and ATP Cycling
ATP can be reformed by phosphorylation, an anabolic
reaction that attaches a phosphate (Pi) group to ADP
• ATP formation requires energy input
ATP cycling is the primary way that cells “earn” and “spend”
energy
• Energy from catabolism of food macromolecules is used to
build ATP
• ATP is broken down and the energy released is used to
power cellular work
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ATP Cycle
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Mitochondria: The Powerhouses of the Cell
The chemical pathway that initiates the breakdown of glucose and
produces some ATP occurs in the cytoplasm
Mitochondria are organelles that synthesize most of the ATP that
cells
need to function
• Have an outer membrane and an inner membrane
Don W. Fawcett/Science Source
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Assess Your Progress 8.2
3. Explain the difference between catabolism and
anabolism.
4. What is a coenzyme?
5. What is ATP, and what is its role in living cells?
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8.3 Obtaining Energy from Carbohydrate
Learning Outcomes
1. Discuss the main chemical pathways of carbohydrate
catabolism.
2. Describe the metabolism of carbohydrates under
anaerobic and aerobic conditions.
3. Explain glycogenolysis and describe how carbohydrates
are stored in the human body.
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Aerobic versus Anaerobic Metabolism
Aerobic metabolism - metabolic pathways for ATP
production that require oxygen
• Occurs in mitochondria if the cell’s oxygen supply is
adequate
Anaerobic metabolism metabolic pathways for ATP
production that do not require oxygen
• Much less energy is made under low-oxygen conditions
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Carbohydrate Metabolism
Normally, human cells rely on glucose, fat, and protein
metabolism to function properly
• Central nervous system (CNS) cells are more dependent
on glucose than fatty acids or amino acids to meet energy
needs
• Most body cells are adaptable and can use multiple
sources of energy
Carbohydrate metabolism will focus on glucose
• Cells can also use fructose and galactose to synthesize
ATP, particularly in the liver
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Glycolysis: Glucose to Pyruvate
Glycolysis - the first phase of glucose catabolism
• Leads to ATP production from glucose oxidation
• Oxidation involves loss of electrons so that energy is transferred to
another molecule
• Possible electrons acceptors in oxidation reactions include:
• The electron shuttles NAD+ and FAD
• Oxygen
• Anaerobic pathway
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Glycolysis
Occurs in cytoplasm
Glucose is broken down to two
molecules of pyruvate, a 3‒carbon
molecule
Two NADH and four ATP molecules
are formed
• Two ATP molecules are used, so
there is a net gain of two
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Fate of Pyruvate: Aerobic Conditions
When plenty of oxygen is
available, pyruvate enters
mitochondria
• Converted to acetyl
coenzyme A (acetyl CoA),
a 2‒carbon molecule
• Two molecules of acetyl
CoA formed from one
molecule of glucose
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Fate of Pyruvate: Anaerobic Conditions
Under anaerobic conditions, pyruvate is converted to lactic
acid, another three-carbon molecule
• Lactic acid releases two H+, forming lactate
• Lactate is released into the bloodstream
• Liver removes lactate from bloodstream and recycles it
into glucose, via a pathway called the Cori cycle
• Liver releases newly made glucose into circulation
• Six ATP are required to make glucose from lactate
• Too inefficient to continue indefinitely
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Fate of Pyruvate in Anaerobic Metabolism
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Coenzymes: Health and Nutritional Significance
The B vitamins thiamin, pantothenic acid, niacin, and
riboflavin are components of coenzymes used in energy
metabolism
• If diet does not supply them in adequate amounts, cells
cannot synthesize coenzymes for catabolism
• Cannot convert enough pyruvate into acetyl CoA to meet energy
needs
• Common symptoms of these deficiencies include fatigue and
weakness
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The Citric Acid Cycle
The oxidation of acetyl CoA is the second phase of glucose
catabolism
The citric acid cycle is a complex series of chemical
reactions that are involved in energy metabolism
• Acetyl CoA is converted to CO2 and H2O
• Occurs twice for each glucose molecule that enters
catabolism (once for each acetyl CoA)
• Oxaloacetate
• Four-carbon molecule that is an important intermediate of the citric
acid cycle
• Coenzymes NAD+ and FAD that pick up hydrogen ions
and high-energy electrons are important products
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Citric Acid Cycle “Initial Reaction”
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Forming Alpha-Ketoglutarate
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Alpha-Ketoglutarate Undergoes Oxidation
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Succinyl-CoA to Fumarate
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Citric Acid Cycle “Ending Point”
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Citric Acid Cycle
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The Electron Transport Chain
Electron transport chain - linked series of enzymes that
synthesize water and ATP during aerobic energy metabolism
• Coenzymes NADH and FADH2 carry hydrogen ions and
high-energy electrons here
• Cytochrome c, a component of the electron transport
chain; facilitates the bonding of hydrogen ions with
oxygen, forming “metabolic water”
• Some energy released during electron transfer is used to
attach a Pi group to ADP, forming ATP
The complete catabolism of one glucose molecule yields
approximately 30 to 32 molecules of ATP
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Electron Transport Chain (ETC)
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Catabolism of Fructose
Fructose is catabolized via the fructolysis pathway
• Occurs only in liver cells
• Fructose is broken down into two products that feed into
the glycolytic pathway, then follow same route as glucose
catabolism
• One of them, glyceraldehyde, can be converted to glycerol
• Glycerol is the backbone of triglyceride molecules
• Fructose is thought to be uniquely fat-promoting compared to other
sugars
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Catabolism of Galactose
Galactose is converted in a two-step process into glucose,
which is then catabolized via the glycolytic pathway
• Conversion of galactose to glucose occurs mainly in liver
• The pathway is also present is some other tissues
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Glycogenolysis
When glucose is not available in
blood, certain cells can obtain it by
glycogenolysis
• Pathway that breaks down
glycogen into glucose
molecules
• Requires coenzyme pyridoxal
phosphate (PLP)
• Primary sites for glycogen
storage and degradation are
liver and muscle tissue
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Skeletal Muscle and Liver Glycogen Stores (Healthy
Average Adult)
Storage Site
Approximate Amount of
Glycogen (g)
Skeletal muscles
325
Liver
90 to 100
TOTAL
415 to 425
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Liver versus Muscle Glycogenolysis
Glycogenolysis occurs in liver when blood sugar levels begin
to fall, such as during an overnight fast
• Liver releases glucose from
glycogen degradation into
the bloodstream for uptake
by cells
Muscle tissue breaks
down glycogen for
glucose catabolism to
occur in muscle cells
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Inborn Errors of Metabolism
An inborn error of metabolism is an inherited metabolic
defect
Glycogen storage disease (GSD) is an inborn error of
metabolism
• Cannot make or degrade glycogen properly
• Abnormal glucose metabolism occurs
• Signs and symptoms include hypoglycemia, fatigue,
irritability, and liver and kidney enlargement
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Alternate Sources of Glucose
Gluconeogenesis is the synthesis of glucose from
noncarbohydrate precursors:
• Glycerol
• Lactate
• Pyruvate
• Many amino acids
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Energy Drinks
Caffeine is a stimulant drug because it increases the activity
of the nervous system
• Can cause unpleasant side effects
Consumption of energy drinks that contain caffeine has
grown in the United States
• Caffeine increases alertness but does not provide any
energy
• May reduce feelings of fatigue but will not lead to having
more energy, unless the beverage contains digestible
carbohydrates
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Catabolism of Glucose for Energy
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Assess Your Progress 8.3
6. What is the primary advantage of aerobic metabolism
over anaerobic metabolism?
7. Distinguish between glycolysis and the citric acid cycle
and the electron transport chain.
8. How is the catabolism of fructose and galactose different
from the catabolism of glucose?
9. Describe the functions of NAD+ and FAD in the production
of ATP.
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8.4 Obtaining Energy from Fat
Learning Outcomes
1. Discuss beta-oxidation.
2. Describe how fatty acids are transformed to enter the
citric acid cycle.
3. Explain ketogenesis and why ketoacidosis can occur in
individuals with poorly controlled diabetes.
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Energy Storage
Triglycerides are the most energy-dense macronutrient group
The body:
• Can extract energy from dietary fat or fat stored in fat
tissue
• Stores more energy in the form of trigylcerides than
glycogen
• Breaks down stored fat for energy when glucose levels are
low
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Approximate Macronutrient Energy Storage (70-kg Adult)
Macronutrient
Fuel Content
(kcal)
Approximate
Percentage of Total
Energy Storage
Fat
140,000
78
Protein
38,000
21
Carbohydrate
2,000
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Fatty Acids Are a Source of Energy
Hormone sensitive lipase (HSL) - enzyme in fat cells
(adipocytes) that removes the three fatty acids from a
triglyceride
• Facilitates lipolysis
• Activated when blood sugar and insulin levels are low
• Glycerol and fatty acids enter bloodstream
• Fatty acids are carried to tissues by albumin, a water-soluble
protein
• Liver can convert glycerol to pyruvate or glucose
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HSL Facilitates Lipolysis in Adipocytes
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Beta Oxidation: Fatty Acids to Acetyl CoA
Fatty acids are catabolized in the mitochondria
• They are “activated” in cytoplasm by binding to coenzyme
A, using energy from 2 ATP
Carnitine is a molecule that helps fatty acids enter the
mitochondria
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Beta-Oxidation 1
Beta-oxidation - chemical
pathway involved in the
catabolism of a fatty acid
• Occurs in mitochondria
• Fatty acid molecules
are cleaved into twocarbon segments that
are converted into
acetyl CoA that enters
the citric acid cycle
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Beta-Oxidation 2
One NADH and one FADH2 are produced each time a twocarbon segment is removed from the fatty acid
• These yield about four ATP when they shuttle electrons
into the ETC
• NADH and FADH2 formed from metabolizing the resulting
acetyl CoA in the citric acid cycle also shuttle electrons to
the ETC, generating even more ATP
• Thus the amount of energy derived from a fatty acid
depends on the length of its carbon chain
• Fatty acids with longer chains contain more chemical energy than
those with shorter chains
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Fate of Acetyl CoA
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Use of Fats for Energy
Human cells cannot use fatty acids to make new glucose
• The glycerol backbone of triglycerides can be converted to
glucose in the liver
An adequate supply of glucose for energy is important
• Red blood cells, the brain, and the nervous system are
more dependent on glucose as a fuel source compared to
other tissues that can use fat as fuel
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Fat Burns in the Absence of Carbohydrate
After a meal, cells use glucose first as an energy source in
order to keep blood sugar levels within a normal range
• Once levels return to normal, cells switch to burn fat for
energy
• Lipolysis and beta-oxidation are inhibited by the presence
of insulin and ATP, and activated by glucagon
• Fatty acid synthesis is activated by insulin and citrate from
carbohydrate metabolism, and inhibited by glucagon
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Ketogenesis
Ketone bodies - acetoacetate, beta-hydroxybutyrate, and
acetone; produced in the liver from acetyl CoA
• They are released into bloodstream
Ketogenesis - ketone body formation
Acetone is eliminated through the breath and has a
distinctive, “fruity” odor
• Levels in breath can be measured to determine if a person
is in early stages of ketosis
Cells, excluding liver cells, can use acetoacetate and betahydroxybutyrate as sources of acetyl CoA
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Ketone Body Formation
When glucose is unavailable (during starvation or periods of
low carbohydrate consumption), most cells can adapt to
catabolize acetoacetate and beta-hydroxybutyrate for energy
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Ketogenic Diet
A ketogenic diet - high-fat, moderate- to low-protein, and
very-low-carbohydrate diet
Ketosis is the formation of excess ketone bodies
• Result of ketogenic diet
• Causes hunger reduction
• Reduces insulin levels, allowing for increased lipolysis and
loss of fat mass
• May be used to treat obesity, metabolic syndrome, type 2
diabetes, epilepsy, Alzheimer’s disease, and cancer
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Ketoacidosis
Ketoacidosis - condition that occurs in the absence of
insulin when excess acetoacetate and beta-hydroxybutyrate
in the bloodstream lower the blood’s pH
• Potentially life-threatening
• Excessive thirst
• Frequent urination
• Blood glucose greater than 250 mg/dL
• “Fruity” odor to breath
• If untreated can lead to coma and death
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Summary of Fat Catabolism
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Assess Your Progress 8.4
10. What happens to fatty acids during beta-oxidation?
11. Describe how cells utilize fatty acids as a source of
energy when glucose is in short supply.
12. Explain the therapeutic benefits and potential
disadvantages of a ketogenic diet.
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8.5 Obtaining Energy from Protein
Learning Outcomes
1. Explain the steps by which proteins can be utilized for
energy.
2. Distinguish between glucogenic and ketogenic pathways.
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Obtaining Energy from Protein
Cells use amino acids to synthesize essential proteins
After these needs are met, cells may catabolize amino acids
for ATP or convert them into glucose or fatty acids
• Glucose and fatty acids are primary energy sources
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Preparing Amino Acids for Catabolism: Removing
Nitrogen
The nitrogen group must be removed before an amino acid
can be used for ATP production
• Removed by deamination or transamination
• Deamination results in production of ammonia, potentially toxic at
high levels
Deamination and transamination require the coenzyme
pyridoxal phosphate (PLP)
• Vitamin B-6 is a component of PLP
• A deficiency negatively affects protein metabolism
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Amino Acids and Energy Metabolism
• Glucogenic amino acids
can be broken down into
either pyruvate or
intermediates of the citric
acid cycle
• Ketogenic amino acids
enter the catabolic
energy pathways as
acetyl CoA
• Some amino acids are
both glucogenic and
ketogenic
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Summary of Using Amino Acids for Energy
The amount of ATP formed
by the catabolism of an
amino acid carbon skeleton
depends on where it entered
the catabolism pathways
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ATP Yields
Alanine
→ 14 ATP
Palmitic acid
→ 106 ATP
Glucose
→ 30-32 ATP
Amino acid catabolism generally yields less energy than the
catabolism of a fatty acid or glucose molecule
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Assess Your Progress 8.5
13. What process must an amino acid undergo before it can
be used for energy?
14. Explain the differences between the glucogenic and
ketogenic pathways of amino acid metabolism.
15. Which molecule would you expect to produce the most
energy: the amino acid lysine, the disaccharide sugar
maltose, or the fatty acid linoleic acid? Explain your
answer.
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8.6 Energy Storage
Learning Outcomes
1. Identify the major sites of energy storage in the body.
2. Describe the process by which triglycerides are stored.
3. Explain what happens to excess carbohydrate when
glycogen stores are full.
4. Explain the fate of excess protein or amino acids.
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Carbohydrate and Fat: Energy Stores in the Body
Macronutrient
Storage Site and Form
Approximate kcal
Stored
Carbohydrate
Liver glycogen
300 – 400
Muscle glycogen
1,200 – 1,600
Adipose cell triglycerides
80,000 – 100,000
Fat
When more fuel is available than necessary to meet
immediate needs, excess sources of energy are stored
• Used when not consuming foods
• The body prefers to use stored fat and glucose
• Only uses body proteins as a last resort
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Storing Triglycerides
After a fat-containing meal, most of the lipids are
incorporated by the liver into very-low-density lipoproteins
(VLDLs), and released into the blood
Lipoprotein lipase is an enzyme that enables adipocytes and
other cells to access lipoproteins’ lipid contents
• Free fatty acids and glycerol enter the cells
• After entering, triglyceride is re-created
• Requires very little energy input
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Storing Glucose
When a person consumes a surplus of glucose, the body
stores excess glucose as either glycogen or triglycerides
Glycogenesis - pathway that links glucose units together for
storage as glycogen
• Occurs in liver and muscle cells
• Specific enzymes bind single glucose molecules together
into long, branched chains of glycogen
• The body stores limited amounts of glycogen
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Fatty Acid Synthesis
Lipogenesis - synthesis of fatty acids
• Two-carbon acetyl CoA units are bound together to form
the hydrocarbon chain of the fatty acid
• The fatty acid elongates and stores energy
When carbohydrates are consumed, glucose is catabolized
to make ATP, inhibiting the breakdown of fatty acids
• As a result, synthesis and storage of triglycerides occurs
in adipocytes
• High carbohydrate consumption can thus result in
accumulation of body fat
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Excess Glucose and Fat Storage
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When Amino Acids Are in Excess
If diet provides an excess of amino acids and cells do not
need energy:
• The liver and kidneys can use glucogenic amino acids to
make glucose (gluconeogenesis)
• Ketogenic amino acids can be converted into acetyl CoA
• Can be used to produce ketone bodies when carbohydrate intake is
limited
• Can feed into lipogenic pathways
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Metabolism: The Fates of Macronutrients and Alcohol
Energy Source
Yields Glucose?
Yields Amino Acids?
Yields Fat?
Amino acids
Yes, except for
ketogenic amino
acids
Yes
Yes
Yes
Yes, only
nonessential amino
acids if N is available
Yes
No, except for the
glycerol backbone
No
Yes
No
No
Yes
Glucose
Triglycerides
Alcohol
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Wasting Excess Energy
As an alternative to energy storage, the body can “waste”
some food energy consumed in excess
Adaptive thermogenesis - process of energy dissipation as
heat that occurs in mitochondria
• Rates change in response to environmental temperature,
diet, and hormones
• Involves activation of uncoupling proteins in mitochondria
that increase heat production at the expense of ATP
production
Nonexercise activity thermogenesis (NEAT) - process by
which energy is expended during spontaneous physical
activity, such as fidgeting
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Assess Your Progress 8.6
16. Trace the path of triglycerides from the liver to storage in
adipose tissue.
17. How does excess carbohydrate consumption increase
body fat deposits?
18. Describe the conversion of amino acids into glucose or
ketones.
19. Discuss the various mechanisms of energy wasting by
the body.
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Did You Know? – Diet Pills
Between 1933 and 1938, a drug call 2,4-DNP, marketed as
Dinitriso and Nitromet, was used as a diet pill for the
treatment of obesity
• Previously used to produce explosives
• Found to have side effect of increasing metabolism when
factory workers lost weight upon exposure
• Works similar to uncoupling proteins
• Quickly banned by the Federal Food, Drug and Cosmetic
Act due to extreme adverse side effects, including death
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8.7 Hormonal Responses to Changing Energy Needs
Learning Outcomes
1. List the key hormones that direct or regulate metabolic
activities.
2. Describe the major effects of metabolic hormones.
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Regulation of Metabolism
If surplus of food energy is consumed, hormones determine
in part whether it is stored or burned
• Hormones are “chemical messengers” secreted by
specific organs
• Circulate through blood to stimulate and regulate cellular activities
of target tissues
The specific actions of each metabolic hormone depend on
the body’s metabolic state:
• Fed, after a meal has been consumed
• Fasted, when a meal has not recently been consumed
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Physiological Effects of Major Metabolic Hormones
Hormone
Overall
Metabolic Effect
Insulin
Anabolic
Increases glycolysis
and glycogenesis
Glucagon
Catabolic
Increases
glycogenolysis and
gluconeogenesis
Cortisol
Catabolic
Epinephrine
Thyroid
Hormone
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Effects in Liver
Effects in Adipose
Tissue
Effects in Muscle
Increases glucose
uptake; increases
lipogenesis
Increases glucose
and amino acid
uptake; increases
glycogenesis and
protein synthesis
Increases
glycogenolysis and
gluconeogenesis
Increases lipolysis
Increases proteolysis
Catabolic
Increases
glycogenolysis and
gluconeogenesis
Increases lipolysis
Regulates
metabolic rate
Increases
glycogenolysis,
gluconeogenesis,
and lipolysis
Increases lipolysis
and lipogenesis
Increases
glycogenolysis
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Insulin: Anabolic Metabolism
When blood glucose levels rise, beta cells in the pancreas
secrete insulin
Insulin attaches to
receptors on cell
membranes of
insulin-responsive cells
• Results in signal to
open glucose transport
proteins in membrane
• Glucose enters the
cytoplasm
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Insulin Promotes Energy Storage
Insulin directs liver and muscle cells to:
• Slow down their glycogenolysis rates
• Increase their rate of glycogenesis
Insulin promotes energy storage:
• Shifts glucose molecules into storage as glycogen in liver
and muscle
• Increases fatty acid uptake and triglyceride synthesis by
adipocytes
• Stimulates protein synthesis in cells
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Actions of Insulin
Insulin promotes
anabolism, such as
glycogenesis,
triglyceride synthesis,
and protein synthesis.
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Glucagon, Cortisol, and Epinephrine: Catabolic
Metabolism
Glucagon, cortisol, and epinephrine are hormones that
instruct cells to use catabolic rather than anabolic pathways
Glucagon is secreted from the alpha cells of pancreas in
response to low blood sugar levels
• Signals liver to increase glycogenolysis and
gluconeogenesis from glucogenic amino acids
• Raises blood glucose levels
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Cortisol
Cortisol - catabolic hormone made in the adrenal glands
• Promotes protein catabolism
• Stimulates the liver to increase use of amino acids for
gluconeogenesis
• Also known as a “stress hormone” because it is released
in stressful situations
• Low blood glucose levels
• Severe injuries
• Physiological states that evoke anxiety or fear
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Epinephrine
Epinephrine (adrenaline) is also produced by the adrenal
glands
• Stimulates catabolism by:
• Increasing glycogenolysis and lipolysis in liver and muscle
• Increasing lipolysis in adipose tissue
• Secreted in large amounts in response to stressful
conditions that increase need for quick energy
• Physical activity
• “Fight-or-flight” situations
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Actions of Catabolic Hormones
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Thyroid Hormone
The thyroid gland at the base of the throat secretes two
hormones collectively called thyroid hormone
• Helps body adapt by increasing or decreasing the rate of
metabolism: can have catabolic or anabolic actions
• Increases rate of glucose catabolism, lipolysis, and protein
synthesis
• Cells can develop and grow normally
• Levels increase during growth and development
• Levels decrease during long periods of starvation or
fasting
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Assess Your Progress 8.7
20. Which hormone(s) promote anabolism, and which
promote catabolism?
21. What conditions stimulate insulin secretion versus
glucagon secretion?
22. Identify pathways that are stimulated by each of the
catabolic hormones.
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8.8 Managing Fuel in the Body
Learning Outcomes
1. List the metabolic responses to short-term and prolonged
fasting.
2. Explain the relationship between insulin resistance and
metabolic syndrome.
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Metabolic Responses to an Overnight Fast
As blood glucose levels fall during early part of an overnight
fast, the pancreas secretes glucagon
• Liver increases glycogenolysis
• Blood glucose levels are maintained
When liver glycogen stores are depleted, glucagon
stimulates gluconeogenesis in liver
• Liver and muscle tissue mainly use fatty acids for fuel
Upon “breaking the fast” with a carbohydrate-rich meal, the
insulin response promotes a shift from a catabolic to an
anabolic state
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Metabolic Responses to Starvation 1
During starvation, where no food or energy is consumed for
an extended period of time, additional changes are made
• Muscle cells rely more heavily on fatty acids for energy
• Adipose tissue increases lipolysis
• Fatty acid levels in blood increase
• Alternative sources of glucose are needed to fuel red
blood cells and nervous tissue
• Liver produces new glucose by gluconeogenesis
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Metabolic Responses to Starvation 2
• Liver cells rely more on ketogenesis
• Converts acetyl CoA to ketone bodies
• Brain starts using ketone bodies for fuel
• Muscle cells begin proteolysis, the breakdown of amino
acids
• The liver can use some of the amino acids for gluconeogenesis
• The breakdown of adipose and muscle tissue causes
extreme weight loss, muscle wasting, and weakness
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Obesity and Insulin Resistance
Insulin binds to the insulin receptor on muscle, fat, and liver
cells
• Allows glucose and fatty acids to be taken up from the
blood and stored
In obesity, the increase in
adipose tissue results in
abnormal metabolic changes
• Cells become unresponsive to
insulin
• Insulin resistance
• Associated with type 2 diabetes
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Nonalcoholic Fatty Liver 1
Excessive alcohol consumption can cause a buildup of fat in
the liver
• Can also occur due to insulin resistance and high fructose
consumption
Insulin-resistant cells do not take up glucose and fatty acids
from the bloodstream or store energy effectively
• Blood glucose levels stay high (hyperglycemia) long after
a meal
• Lipolysis in adipocytes is not restricted
• Excess fatty acids released into bloodstream
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Nonalcoholic Fatty Liver 2
Influx of glucose and fatty acids stimulates triglyceride
synthesis in the liver
• Nonalcoholic fatty liver (NAFLD) - abnormal
accumulation of fat in the liver that is not caused by
alcohol consumption
• High fructose intake may contribute to the increasing
incidence of NAFLD
• Fructose can only be catabolized in the liver
• Excess consumption can rapidly promote lipogenesis and fat
accumulation
• Fatty liver a sign of impending liver damage
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Metabolic Syndrome
When liver cells become insulin resistant, their ability to
regulate glycogen synthesis and gluconeogenesis becomes
altered
Metabolic syndrome can occur as a result
• Glucose still produced in liver and released into
bloodstream
• Blood glucose levels rise
• Pancreas secretes more insulin
Excess body fat is a major risk factor for metabolic syndrome
and type 2 diabetes
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Assess Your Progress 8.8
23. Discuss the metabolic processes that occur during an
overnight fast.
24. List the major metabolic responses that occur in muscle,
adipose tissue, and the liver during starvation.
25. Explain why insulin resistance may lead to the
development of nonalcoholic fatty liver disease and
metabolic syndrome.
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8.9 Putting the Metabolism Puzzle Together
Learning Outcomes
1. Summarize the catabolic and anabolic pathways and
actions of glucose, fat, and amino acids.
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Energy Metabolism Summary
Macronutrient
Carbohydrate
Fat
Protein
Catabolism
Anabolism
Pathways:
Pathways:
Glycolysis
Gluconeogenesis
Glucose → Pyruvate
Pyruvate → Glucose (certain cells)
Glycogenolysis
Glycogenesis
Glycogen → Glucose
Glucose → Glycogen
Pathways:
Pathways:
Beta-oxidation
Fatty acid synthesis
Fatty acids → Acetyl CoA
Acetyl CoA → Fatty acids
Lipolysis
Lipogenesis
Triglycerides → Glycerol + Fatty acids
Fatty acids + Glycerol → Triglycerides
Pathways:
Pathways:
Proteolysis
Protein synthesis
Proteins → Amino acids
Amino acids → Proteins
Deamination
Amino acids → Carbon skeletons
Gluconeogenesis
Transamination
Amino acids → Glucose
Amino acids → Carbon skeletons
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Summary of Energy Metabolism
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Sustainability and Your Diet
Fossil fuels are made from decomposed plant and animal
material that formed over millions of years
• Only available in finite amounts, so there is a need for
sustainable energy sources that cannot be depleted
Renewable energy sources are self-regenerating, but are
also flow-limited: they can be constant yet limited in how
much energy they can produce in a certain period of time
• Combining various renewable energy sources can
contribute to a sustainable energy system while reducing
greenhouse gas emissions from the burning of fossil fuels
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Assess Your Progress 8.9
26. Explain the differences between glycogenesis and
glycogenolysis and between lipogenesis and lipolysis.
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8.10 Alcohol as an Energy Source
Learning Outcomes
1. List the amounts of beer, wine, and hard liquors in a
standard drink.
2. Explain how alcohol can be metabolized and utilized for
energy.
3. Identify factors that affect alcohol absorption and
metabolism.
4. Discuss the effects of alcohol on the body and health.
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Ethanol
Ethanol - a simple, two-carbon molecule that is more commonly
called “alcohol”
• Soluble in water
Beer and wine contain simple carbohydrates and small amounts of
certain minerals and B vitamins
Hard liquors have essentially no nutritional value other than water
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A Standard Drink
A standard drink contains 13 to 14 g of alcohol; it is
approximately:
• 12 ounces of beer
• 5 ounces of wine
• 1 ½ ounces of liquor
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Alcohol Absorption and Metabolism 1
The stomach and small intestine rapidly absorb alcohol
• Absorption slowed if alcohol is consumed with meals
• Absorption is faster if alcohol is in carbonated beverages
or mixed with soft drinks
• Provides 7 kcal/g, but is not a nutrient
• When consumed in excess, can damage every organ and
cause death
• To reduce the harmful effects of alcohol, the body
detoxifies the simple molecule by converting it into less
damaging compounds
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Alcohol Absorption and Metabolism 2
Gastric alcohol dehydrogenase - enzyme that detoxifies
some alcohol while it is in the stomach
Liver is primary site for metabolism of absorbed alcohol
• A moderate drinker can metabolize 12 to 15 g of alcohol
(approximately 1 standard drink) per hour
• Excess circulates in bloodstream until liver can metabolize
it
Blood alcohol concentration (BAC) - percentage that
reflects the concentration of alcohol in the bloodstream
• In the USA, a BAC of 0.08% is the legal limit for
intoxication for automobile operators who are 21 years of
age or older
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Alcohol Dehydrogenase Pathway
Alcohol dehydrogenase pathway - catabolic pathway that
metabolizes alcohol in the liver
Acetaldehyde - highly toxic substance formed during the
first step of the alcohol dehydrogenase pathway
Aldehyde dehydrogenase - enzyme that helps convert
acetaldehyde to acetate, a less toxic substance
• Acetate can be converted to acetyl CoA, which can enter
citric acid cycle or be used in fatty acid or ketone body
synthesis
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Microsomal Ethanol-Oxidizing System
Microsomal ethanol-oxidizing system (MEOS) secondary pathway for processing alcohol in the liver
• Used when excessive amounts of alcohol are consumed
• Also produces acetaldehyde that is processed to yield
acetyl CoA
• Wastes energy in the form of heat
• Causes vasodilation in alcoholics, who thus are at risk of
hypothermia
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Factors That Influence Alcohol Metabolism
Several factors account for the variability in alcohol
metabolism:
• Amount of alcohol
• Timing of consumption
• Sex
• Body size and composition
• Age
• Prior drinking history
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Alcohol Consumption and Approximate BACs
Image Source; Purestock/SuperStock
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Did You Know? – Alcohol and Gout
Excess alcohol intake can interfere with the kidneys’ ability to
excrete uric acid, a by-product of nucleic acid (DNA and
RNA) metabolism
• Uric acid accumulates in bloodstream and can form tiny,
needlelike crystals in body fluids
• The crystals contribute to the signs and symptoms of gout
• Extremely painful form of arthritis that often causes inflammation in
the joints of the toes
• People with gout should avoid drinking excess alcohol
because it aggravates their condition
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Did You Know? – Hangovers
Drinking alcohol at a rate that exceeds the body’s ability to
metabolize it may experience a hangover the next day
• The headache and nausea, sensitivity to light and noise,
fatigue, and thirst are in part explained by the
accumulation of acetaldehyde in various tissues
• If a person were to consume just 1 teaspoon of pure
acetaldehyde through the mouth, they would experience
an instant hangover
• The toxic effects of alcohol on the brain, and alcohol’s
dehydrating and hypoglycemic effects, are also thought to
contribute to the discomfort
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Effects of Alcohol on Liver Metabolism 1
Alcohol directly affects the liver by disrupting the normal
metabolism of glucose, fatty acids, and amino acids
The two dehydrogenase reactions in alcohol metabolism
result in the transfer of an electron to NAD+, producing NADH
NADH accumulates and NAD+ becomes depleted, changing
the ratio of NADH to NAD+, which affects normal metabolic
pathways in liver cells:
• The rate of glycolysis slows
• More pyruvate is converted to lactic acid
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Effects of Alcohol on Liver Metabolism 2
• ATP production from glucose is impaired
• Can lead to hypoglycemia because not enough NAD+ is
available to maintain normal gluconeogenesis rate
• Due to lack of NAD+, the activity of the citric acid cycle
slows
• Some acetyl CoA molecules enter the citric acid cycle for
energy
• Liver cells use most of the excess acetyl CoA to make fatty acids for
triglyceride synthesis
• Accumulation of triglycerides in liver cells can cause “alcoholic fatty
liver”
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Effects of Alcohol Metabolism on the Liver
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Cirrhosis of the Liver
If a person with a fatty liver continues to consume alcohol,
they are likely to eventually develop cirrhosis of the liver
• Condition characterized by the accumulation of scar tissue
in the liver, which permanently damages the organ
Arthur Glauberman/Science Source
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Alcohol’s Effects on the Body
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Typical Effects of Alcohol at Various BAC Levels (Adults)
Blood Alcohol
Concentration
0.02
Physiological and Psychological Effects
Some loss of good judgment, altered mood, relaxation
0.05
Reduced inhibitions, resulting in exaggerated emotional
and behavioral responses to situations
Impaired judgment, good mood
0.08
Loss of balance, slower-than-normal reaction time,
impaired memory
Reduced ability to control behavior
0.10
0.15
Major impairment of hearing, vision, and muscular
coordination
Slurred speech and obvious delayed reaction time
0.20
Poor muscular control, vomiting, loss of balance
Cannot walk without assistance, mental confusion
May pass out
0.25 or above
Loss of consciousness, coma, possible death from
respiratory arrest (breathing stops)
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Classifying Drinkers
Classification of
Drinker
Amount of Alcohol Consumed (Standard Drinks)
Moderate
Males
Up to 2 drinks/day
Females
Up to 1 drink/day
Heavy
15 or more drinks/week
8 or more drinks/week
Binge
5 or more drinks/occasion
(about 2 hours)
4 or more
drinks/occasion (about 2
hours)
The 2020-2025 Dietary Guidelines for Americans emphasize the
importance of limiting alcohol consumption to moderate intakes
• Regular consumption of alcoholic beverages can make it
difficult to stay within recommended calorie intake and may
increase consumption of added sugars
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Alcohol Use Disorder
A “problem drinker” experiences problems at home, work,
and school that are associated with their drinking habits
• According to the National Institutes of Health (NIH), a
person with a severe drinking problem has an alcohol use
disorder (AUD)
• Problem drinkers and people with an AUD engage in
behaviors that place themselves and others in danger,
such as drinking and driving
• According to estimates, 5% of Americans who were 12
years of age and older had an AUD in 2018
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Signs of Problem Drinking
You might be at risk of an alcohol use disorder if you:
• Drink to relax, forget your worries, or improve your mood
• Lose interest in food as a result of your drinking habits
• Binge drink
• Lie about your drinking habits or try to hide them
• Drink alone
• Hurt yourself or someone else while drinking
• Were drunk more than three or four times last year
• Need to drink more alcohol than you used to drink to get “high”
• Feel irritable when you are not drinking
• Have medical, social, or financial problems caused by drinking habits
• Have been cited for driving while intoxicated (DWI) or driving under
the influence of alcohol (DUI)
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Caffeinated Alcoholic Beverages
Caffeinated alcoholic beverages (CABs) are commercially
available drinks that are popular among younger drinkers
• Mixing caffeine and alcohol can be dangerous
• Caffeine can mask some of the effects of alcohol by
increasing feelings of alertness.
• Those consuming CABs may not realize their level of impairment,
which can increase the risk of overconsumption
• The caffeine in the beverages does not affect the body’s
ability to metabolize alcohol
• The person’s BAC will not be reduced as a result of drinking CABs
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Assess Your Progress 8.10
27. Describe the two major pathways that the body uses to
metabolize alcohol.
28. Summarize the effects of alcohol on the liver.
29. What is BAC? What is the legal limit for BAC in the
United States?
30. Describe at least two effects of alcohol on the body.
31. List three signs that a problem drinker may have an
alcohol abuse disorder.
32. Why is consuming alcohol mixed with caffeine more
dangerous than alcohol alone?
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Case Study 1
Energy drinks and fatigue
• In an attempt to manage his hectic schedule, Eric often
skips breakfast and consumes an energy drink instead.
Then, he usually eats a large lunch and dinner later in the
day. However, lately, Eric has been working at night and
replacing his dinner with an energy drink as well. The
drinks contain mostly water with small amounts of added
sugars, sucrose and glucose, caffeine, and several Bvitamins. After replacing his dinner meal with an energy
drink for 2 weeks, Eric has reported feeling fatigued and
weak.
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Case Study 2
1. What is the most probable reason Eric been experiencing
fatigue recently?
2. Explain the different sources of energy in the diet.
3. When Eric is not eating, where is his energy coming
from? Explain how metabolism changes between the fed
and fasted states.
4. Do you think Eric can sustain this change to his diet?
Why or why not?
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Accessibility Content: Text Alternatives for Images
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Metabolism 2 - Text Alternative
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Food macronutrients undergoes catabolic reactions and produce usable
energy, heat energy, and small molecules such as glucose, amino acid,
carbon dioxide, and water. The usable energy and small molecules
undergoes anabolic reactions and produce cell macromolecules.
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Energy Shuttles: NAD+ and FAD - Text Alternative
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NAD with the addition on two hydrogen ions and electrons is converted
into NADH plus Hydrogen ion.
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ATP Cycle - Text Alternative
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ATP releases energy and yields ADP plus phosphate. ADP plus
phosphate converted into ATP using the energy.
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Glycolysis - Text Alternative
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6-carbon glucose is converted into 6-carbon glucose with phosphate by
converting ATP to ADP. 6-carbon with phosphate is converted to 6-carbon
with 2-phosphate by converting ATP to ADP. 6-carbon with 2-phosphate is
divided into two parts each with 3-carbons with a phosphate. 3-carbon
with a phosphate is converted into 3-carbon with 2-phosphate by
converting NAD plus phosphate to NADH plus hydrogen ion. 3-carbon
with 2-phosphate is convereted to 3-carbon with a phosphate by
converting ADP to ATP releases water and again converts ADP to ATP in
the further process and yields 3-carbon (Pyruvate).
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Fate of Pyruvate: Aerobic Conditions - Text Alternative
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Pyruvate converts NAD to NADH plus hydrogen ion and undergoes
addition of TPP, CoA, and removal of carbon dioxide and yields Acetyl
CoA.
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Fate of Pyruvate in Anaerobic Metabolism - Text
Alternative
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The glucose in liver enters the glycogen in liver and the blood stream and
inside the cell. This glycogen in the cell is converted into pyruvate and
ATP. Pyruvate yields lactic acid. The lactic acid releases hydrogen ions
and yields lactase which enters the blood stream and passed to the liver.
The data represented are as follows: 1. In anaerobic conditions, muscle
cells rapidly metabolize glucose to lactic acid and then to lactate. 2.
Lactase enters the blood stream. 3 a. The liver can remove lactate from
blood, convert it into glucose (via Cori cycle), and release the simple
sugar into the bloodstream, if the fuel is needed. 3 b. Certain cells can
remove lactate from the bloodstream and metabolize it for energy. 4. If
the body does not need the energy, the liver converts glucose to
glycogen.
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Citric Acid Cycle - Text Alternative
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Pyruvate converts NAD to NADH plus hydrogen ion and undergoes
addition of TPP, CoA, and removal of carbon dioxide and yields Acetyl
CoA. The Acetyl CoA enter the cycle by releasing CoA. Citrate converts
NAD to NADH plus hydrogen ion, release carbon dioxide and yields
alpha-ketoglutarate which converts NAD to NADH plus hydrogen ion,
release carbon dioxide and yields Succinyl-CoA. Succinyl-CoA releases
CoA and cycles between GTP and GDP by converting ADP to ATP and
yields Succinate. Succinate converts FAD to FADH2 and yields Fumarate
which yields Malate with the addition of water. Malate converts NAD to
NADH plus hydrogen ion and yield oxaloacetate.
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Electron Transport Chain (ETC) - Text Alternative
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The electron transport chain has an inner mitochondrial membrane and a
cytochrome c in between the amino acids. The NADH and FADH2
provided the electrons to the amino acids and release NAD and FAD. The
electrons are transported to the following amino acids with the help of
energy and release water and produce energy by converting ADP to ATP.
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Liver versus Muscle Glycogenolysis - Text Alternative
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The glycogen in the liver produce glucose and passed on to the blood
stream. The glycoge in muscles produce glucose intermediate and does
not release glucose.
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Alternate Sources of Glucose - Text Alternative
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Glycerol in the liver produce glucose and pyruvate. Glucose converts into
blood glucose. Pyruvate with the addition of lactate enters citric acid cycle
which involves glycogenic amino acids and passed to glucose with the
addition of energy.
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Catabolism of Glucose for Energy - Text Alternative
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Phase I: In cytoplasm, glucose release hydrogens and electrons and
converted into glycolysis which release ATP. Glycolysis pyruvate in
mitchondria which releases carbondioxide, hydrogens, electrons, and
yields AcetylCoA. Phase 2: AcetylCoA converts oxaloacetate to citrate.
The citric acid cycle releases 2 carbon dioxide molecules, ATP, hydrogen
and elctron. Phase 3: The hydrogens and electrons released by
glycolysis, pyruvate, and citric acid cycle enters the electron transport
chain which produce ATP and releases the hydrogens and electrons to
convert 1/2 O 2 to water.
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HSL Facilitates Lipolysis in Adipocytes - Text Alternative
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The fat cell has the outer layer of adipocyte. The parts inside the cells are
triglyceride, HSL, glycerol, fatty acids. They enter the blood stream and
forms albumin.
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Beta Oxidation: Fatty Acids to Acetyl CoA - Text
Alternative
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In cytoplasm, fatty acids and acetyl CoA converts ATP to ADP and the
fatty acid is bonded to the acetyl CoA, then passes through the outer
mitochondrial membrane via cartinine to the intermembrane space then
passes through the inner mitochondrial membrane within the
mitochondria.
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Beta-Oxidation 1 - Text Alternative
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The data represented are as follows: Enzymes cleave a 2-carbon
segment of fatty acid chain. Two-carbon segment form AcetylCoA and
hydrogen ions are picked up by carrier molecules FAD and NAD+. Steps
1 and 2 repeat until only a 2-carbon segment (acetyl CoA remains).
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Ketone Body Formation - Text Alternative
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The Acetyl CoA enter the citric acid cycle alos undergoes a reversible
reaction and yields Acetoacetate that releases carbon dioxide and yields
Acetone which is exhaled by lungs. The Acetoacetate also undergoes a
reversible reaction and yields Beta-hydroxybutyrate.
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Summary of Fat Catabolism - Text Alternative
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The data represented are as follows: Hormone sensitive lipase facilitates
removal of fatty acids from triglycerides. Albumin transports fatty acids in
the bloodstream and releases them for uptake into cells, particularly
muscle cells. Fatty acid binds to coenzyme A. The activated fatty acids
enter the mitochondria with the help of carnitine. Fatty acids are
catabolized by beta-oxidation. Acetyl CoA molecules enter the citric acid
cycle and are catabolized. Carriers transport electrons to electron
transport chain, and ATP synthesis occurs.
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Amino Acids and Energy Metabolism - Text Alternative
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The data represented are Carbon skeletons of Pyruvate: Alanine,
Cysteine, Glycine, Serine, Threonine, Tryptophan. Carbon Skeletons of
alpha-ketoglutarate: Glutamate, Arginine, Glutamine, Histidine, Proline.
Carbon skeletons of intermediate: Methionine, Valine, Threonine,
Isoleucine. Carbon skeletons of intermediate: Tyrosine, Phenylalanine.
Carbon skeletons of oxaloacetate: Asparagine, Aspartate. Carbon
Skeletons of Acetyl CoA: Isoleucine, Threonine, Tyrosine, Leucine,
Lysine, Phenylalanine, Tryptophan.
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Summary of Using Amino Acids for Energy - Text
Alternative
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Amino acid leads to carbon skeleton which leads to another carbon
skeleton which leads to Pyruvate, Acetyl CoA, and citric acid cycle
intermediated which release ATP.
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Excess Glucose and Fat Storage - Text Alternative
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The glucose produce Acetyl CoA and fatty acids. The fatty acids don't
produce ATP but Triglycerides which produce adipocyte.
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Actions of Insulin - Text Alternative
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Amino acids produce protein, fatty acids and glycerol produce
triglycerides, glucose produce glycogen. Muscle cell has glucose.
Adipocyte has glucose and fatty acids. Glucose enters the insulin
responsive cell where carbon dioxide and water produce ATP. The liver
cell has glucose, glycogen, and triglycerides.
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Actions of Catabolic Hormones - Text Alternative
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Proteins has amino acids, triglycerides has fatty acids and glycerol,
glycogen has glucose. Adipocyte has fatty acids and glycerol. Muscle cell
has amino acids. Fatty acids and ketone bodies enter a cell where carbon
dioxide and water produce ATP. Pyruvate, lactate, glycerol and amino
acids in liver produce ketone bodies, glucose and glycogen.
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Obesity and Insulin Resistance - Text Alternative
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The muscle of fat cell membrane has a non responsive insulin receptor
where the insulin attached and a insulin-resistant glucose transporter.
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Summary of Energy Metabolism - Text Alternative
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Glucose leads to pyruvate that leads to Acetyl CoA which enter citric acid
cycle. The glucose produce glycogen, glycerol, pyruvate produce lactate,
glycerol, and amino acids. Acetyl CoA produce 3-fatty acids, ketone
bodies, alcohol, and amino acids. Citric acid cycle produce pyruvate,
glucose, amino acids. Amino acids produce protein. Triglycerides produce
glycerol and 3-fatty acids.
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Alcohol Consumption and Approximate BACs - Text
Alternative
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The column headers are Male 170 lobes, blood alcohol concentration
(percentage), female 140 lobes. The percentage ranges from 0.01 to 0.10
in which 0.08 is legal limit. 0.03-for male 2 glasses. 0.05-for male 3
glasses, for female 2 glasses. 0.07-for male four glasses. 0.08-for female
3 glasses. 0.10-for male 5 glasses.
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Effects of Alcohol Metabolism on the Liver - Text
Alternative
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The NAD and NADH in liver cell creates pyruvate which produce lactic
acid but not Acetyl CoA. The blood glucose level decreases due to slow
rate of glycogenesis and the NADH enter the citric acid cycle. Due to lack
of NAD slows the citric acid cycle and the alcohol produce acetyl CoA
and enter the citric acid cycle and the acetyl CoA produce fatty acids.
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Alcohol’s Effects on the Body - Text Alternative
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The data represented are as follows: Brain: Impairs brain functioning and
damages brain; increases risk of stroke. Mouth, throat, voice box:
Increases risk of cancer. Esophagus: Increases risk of cancer of the
esophagus. Skin: Causes flushing of skin and heat loss. Breast:
Increases risk of breast cancer. Heart: Damages heart muscle, resulting
in enlargement of the heart and heart failure; causes hypertension.
Stomach: Irritates stomach lining and increases risk of stomach cancer.
Liver: Causes liver cells to fill with fat, eventually resulting in hepatitis,
cirrhosis, and liver failure; increases risk of liver cancer. Pancreas:
Impairs pancreatic function, can cause inflammation of the pancreas, and
increases risk of pancreatic cancer. Small intestine: Interferes with
nutrient absorption. Abdomen: Increases fat deposits in abdominal
region. Colon and rectum: Increases risk of colon and rectal cancer.
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